1. Field of the Invention
The present invention relates to a bending tool for bending sheet metal and particularly to a bending die cooperating with a bending bar connected to the ram of a press brake. The bending bar has a tapered edge cooperating with a longitudinal groove on the top of the bending die, and the bending angle may be adjusted by varying the depth of the longitudinal groove.
2. The Prior Art
In the U.S. Pat. No. 3,844,156, there is provided a bending tool for bending sheet metal which comprises a lower female bending die operating in conjunction with an upper male bending die, the bending bar. The side of the lower bending die that faces the upper die comprises a longitudinal groove, the cross section of which can in principle be configured according to individual requirements. In the so-called "free bending", the sheet of metal to be bent lies with one side against two straight edges on the bottom die and along one straight edge on the top die. The acuteness of the angle formed in the sheet is dependent on the distance by which the upper die penetrates into the groove provided in the lower die. It has been further proposed that the bottom of the groove in the lower die be provided with an arrester strip by means of which the penetration distance from the said bottom to the surface of the die can be adjusted. Thereby the bending angle of the sheet metal to be processed can be varied. It was feasible to furnish the bottom surface of the longitudinal groove over its entire length with a number of adjacently arranged inclined surfaces. Consequently, the lower surface of the arrester rail exhibits a corresponding number of oblique surfaces cooperating with the oblique surfaces of the bottom of the longitudinal groove. In this manner a saw-toothed wedge system was formed by means of which the height of the lower die groove base was changed by moving the lower wedge relative to the upper wedge. The groove base was formed either by the arrester rail or by vertically moveable pins. This arrangement has proved to be very successful.
However, in connection with precision work, the disadvantage arises that in the vicinity of the gaps that are formed when the two wedges are moved in opposite directions, undesirable deflections occur as a result of the heavy loading which is exerted by the bending ram of the press.